print head

Abstract

A method for operating an actuator unit for a print head, the actuator unit comprising a first piezoelectric element connected to a first potential and a third potential, and a second piezoelectric element connected to a second potential and the third potential, wherein the actuator unit is configured to deflect when the first potential and the second potential have the same polarity with respect to the third potential, the method comprising the steps of: applying a first variable high voltage, Vt, between the first potential and the third potential; applying a second variable high voltage, Vb, between the second potential and the third potential; and applying a switchable ground connection to the third potential.

Description

[Technical Field]

[0001] The present invention relates to a print head, preferably a print head for a 3D printer or a 2D printer. More specifically, the present invention relates to an actuator for the print head, a fluid system for the print head, and a method for driving the actuator. [Background technology]

[0002] Examples of 3D print heads are disclosed, for example, in patent applications EP 3 825 100 A1, EP 21 215 072.6, and EP 21 212 024.0, all of which are incorporated herein by reference. In particular, the same names and definitions as in the aforementioned applications are used wherever possible. However, the same print heads may be placed in a 2D printer.

[0003] The main principle of a printhead is that the material is first stored in a reservoir, preferably in a liquid phase. The material, also called a fluid or liquid, is then transported to and / or into the printhead via conduit elements, such as pipes, tubes, or connector elements.

[0004] In the printhead, the fluid is further transported into the pressurized region. A portion of the fluid is then ejected from the pressurized region through the nozzle opening in the nozzle plate. This ejection is caused by the movement of the actuator and the displacement of the liquid within the pressurized region, preferably via an extension member attached to the actuator.

[0005] The displacement of the material caused by the displacement of the extension member results in localized and transient positive pressurization of the liquid material within the ejection region. The shape region sandwiched between one or more of the lower surfaces displaced by the displacement of the extension member and the shape region formed on the upper surface of the nozzle plate and / or spacing plate by their orthogonal projection may be referred to as the ejection region, and may be additionally referred to as a virtual chamber when experiencing a portion of positive pressurization within a larger pressurized region.

[0006] To improve overall performance and enable high native resolution printing with high-viscosity inks, the mechanical and electrical actuator designs and / or fluid designs of the printhead may be optimized.

[0007] In detail, improved material transport designs within the printhead enhance printing efficiency and capabilities. This includes printing with inks that settle and / or aggregate, or printing with printheads angled relative to gravity.

[0008] Furthermore, simplifying the structural design of printhead elements reduces the structural complexity of the printhead, particularly the material circulation system, and therefore the complexity of assembly. As a result, one or more of the following are improved: printing efficiency, capacity, and cost efficiency.

[0009] Furthermore, improved electrical and / or electrical signal designs enable more efficient motion and new motion modes. Therefore, printing efficiency is improved. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention is described in the appended claims. Embodiments, subjects, aspects, and / or examples in the following description that are not covered by the appended claims are deemed not to be part of the present invention. [Means for solving the problem]

[0011] According to one aspect of the present invention, a print head for a printer is provided. The print head comprises a first housing element including at least two first channel structures, the first channel structures extending in a first direction and configured to transport a liquid material. A second housing element is located below the first housing element and includes a plurality of second channel structures, the second channel structures extending in a second direction substantially perpendicular to the first direction and configured to transport a liquid material. Each second channel structure overlaps one portion of the first channel structure and at least one further portion of the first channel structure, for liquid communication of a liquid material between two or more portions of the first channel structures.

[0012] The first housing element is also referred to as the main fluid plate. The second housing element is also referred to as the spacing plate.

[0013] In one embodiment of the present invention, the print head further comprises a plurality of extension members projecting from the actuator through respective openings within a first housing element, in directions substantially perpendicular to a plane defined by a first direction and a second direction, the extension members being arranged substantially parallel to each other and substantially forming a line in the first direction.

[0014] In one embodiment of the present invention, each second channel structure is configured to form an ejection region below each end portion of the extension member.

[0015] In one embodiment of the present invention, the print head further comprises a nozzle plate located below a second housing element, the nozzle plate having nozzle openings for ejecting liquid material, the nozzle openings preferably positioned corresponding to the location of the ejection region, and the print head is preferably configured to eject liquid from the ejection region through the respective nozzle openings based on the operation of the respective extension members.

[0016] In one embodiment of the present invention, the print head further comprises a membrane element provided below the first housing element and above the second housing element, and the membrane element seals the first housing element from the second housing element at least in the region of the end portion of the extension member, and is configured to form a pressurized region in the second channel in said region.

[0017] In one embodiment of the present invention, the print head further comprises a heating element, and the heating element is provided a) within the first housing element, b) below the first housing element and above the membrane element, or c) below the first housing element and below the membrane element.

[0018] In one embodiment of the present invention, the membrane element includes a shaped portion at the end portion of the extension member, and the shaped portion is configured to conform to the shape of the end portion of the extension member or an intermediate element attached to the end portion of the extension member.

[0019] In one embodiment of the present invention, one or more additional reference elements are provided on the free actuator end portion to define the position where the extension member protrudes.

[0020] In one embodiment of the present invention, at least one of the first channel structures is configured as an inlet channel and is preferably connected to an inlet connector, and at least one other first channel structure is configured as an outlet channel and is preferably connected to an outlet connector.

[0021] In one embodiment of the present invention, the cross-section of the inlet channel continuously decreases from one end to the other along the material transport direction, and / or the cross-section of the outlet channel continuously increases from one end to the other along the material transport direction.

[0022] In one embodiment of the present invention, an upper clamping element and / or a lower clamping element configured to limit the movement of the actuator are provided at the central position of the actuator.

[0023] In one embodiment of the present invention, the first channel structure and / or the second channel structure are formed by at least one of the following methods: etching, laser ablation, injection molding, or milling.

[0024] In one embodiment of the present invention, one or more junction portions for connecting each channel structure are formed in at least one of the first channel structures and are connector elements.

[0025] In one embodiment of the present invention, at least one bypass channel is formed to connect at least two of the first channel structures.

[0026] According to one aspect of the present invention, a method for assembling a print head is provided. The method includes providing a first housing element comprising at least two first channel structures, the first channel structures extending in a first direction and configured to transport a liquid material, and arranging a second housing element below the first housing element, the second housing element comprising a plurality of second channel structures, the second channel structures extending in a second direction substantially perpendicular to the first direction and configured to transport a liquid material, the second housing element being arranged such that each second channel structure overlaps one portion of the first channel structure and at least one further portion of the first channel structure, for liquid communication of a liquid material between two or more portions of the first channel structures.

[0027] According to one aspect of the present invention, an actuator unit for a print head is provided. The actuator unit comprises a first piezoelectric element and a second piezoelectric element provided on opposing surfaces of a spacing element, wherein the surfaces of the first and second piezoelectric elements not facing the spacing element are connected to a first potential and a second potential, respectively, preferably a high-voltage signal, and the surfaces of the first and second piezoelectric elements facing the spacing element are connected to a third potential, preferably a switchable ground potential, and the first and second piezoelectric elements are configured such that, when the first and second potentials have the same polarity with respect to the third potential, one contracts and the other expands in a direction parallel to the surface facing the spacing element.

[0028] Spacing elements are also referred to as stiffening elements. The first piezoelectric element is preferably an upper piezoelectric element, and the second piezoelectric element is preferably a lower piezoelectric element.

[0029] In one embodiment of the present invention, the first piezoelectric element and the second piezoelectric element have the same polar axis direction.

[0030] In one embodiment of the present invention, the actuator unit has a thickness direction, a width direction, and a length direction longer than the width direction, the first piezoelectric element and the second piezoelectric element are provided in the thickness direction on the spacing element, and the polar axes of the first piezoelectric element and the second piezoelectric element are configured such that their respective d31 mode deformations are in the length direction of the actuator.

[0031] In one embodiment of the present invention, the first potential and the second potential originate from the same high-voltage signal.

[0032] In one embodiment of the present invention, an electrode is provided on at least one surface of the first piezoelectric element (302) and the second piezoelectric element (303), and the electrode is preferably a thin-film electrode.

[0033] In one embodiment of the present invention, one end of the actuator in the longitudinal direction is fixed to the print head, and the other end is a free end.

[0034] In one embodiment of the present invention, an extension member protrudes from one side of either the first piezoelectric element or the second piezoelectric element at the free end of the actuator.

[0035] In one embodiment of the present invention, the spacing element is a stiffening element and is configured to increase the rigidity of the actuator.

[0036] In one embodiment of the present invention, the spacing element is made from a non-conductive material, preferably one or more of the following: glass fiber material, carbon fiber material, metal oxide material, composite material, or ceramic material.

[0037] In one embodiment of the present invention, the first piezoelectric element (302) and the second piezoelectric element (303) are made from one or more modifications of lead zirconate titanate and PZT.

[0038] According to one aspect of the present invention, an actuator block for a print head is provided. The actuator block comprises a plurality of actuator units as described in any one of the embodiments, arranged substantially parallel to the width direction of the actuator units, and the respective first, second, and third potentials of each actuator unit are controlled via a controller having separate outputs for each actuator unit.

[0039] In one embodiment of the present invention, the actuator units are arranged in a sawtooth arrangement having a longitudinal orientation of the actuator units.

[0040] According to one aspect of the present invention, an actuator assembly for a print head is provided. The actuator assembly comprises a plurality of actuator blocks as described in the aspect, arranged substantially parallel to the width direction of the actuator unit.

[0041] According to one aspect of the present invention, a method for an actuator unit described in any one of the embodiments is provided. The method includes applying a first variable high voltage Vt between a first potential and a third potential, applying a second variable high voltage Vb between a second potential and a third potential, and applying a switchable ground connection to the third potential, wherein the first variable high voltage Vt and the second variable high voltage Vb are the same variable high voltage, preferably positive or negative.

[0042] In one embodiment of the present invention, the first and second voltages and ground connection states are selected such that the displacement of the actuator is less than the speed of sound of the liquid material ejected from the print head.

[0043] According to one aspect of the present invention, a method is provided for operating an actuator unit for a print head. The actuator unit comprises a first piezoelectric element connected to a first potential and a third potential, and a second piezoelectric element connected to a second potential and a third potential, wherein the actuator unit is configured to bend when the first and second potentials have the same polarity with respect to the third potential, and the method includes applying a first variable high voltage Vt between the first potential and the third potential, applying a second variable high voltage Vb between the second potential and the third potential, and applying a switchable ground connection to the third potential.

[0044] In one embodiment of the present invention, the first variable high voltage Vt and the second variable high voltage Vb are the same variable high voltage, and are preferably positive or negative voltages.

[0045] In one embodiment of the present invention, the first variable high voltage Vt and the second variable high voltage Vb are discretely switchable between n states.

[0046] In one embodiment of the present invention, n is between 2 and 200, and more preferably between 3 and 150.

[0047] In one embodiment of the present invention, the switchable grounding connection has the following two states: a) A first state in which the earth connection is connected, allowing current to flow from the respective first and second potentials, generating an electric field across each piezoelectric element, thereby causing deformation of them, preferably d31 mode deformation. b) A second state in which the ground connection is disconnected, preventing current from flowing from the respective first and second potentials, thereby preventing the generation of an electric field across each piezoelectric element and thus preventing deformation.

[0048] In one embodiment of the present invention, the maximum upward deflection ADn corresponds to the ground connection in the connected state and the maximum positive voltages Vb and Vt, while the maximum downward deflection AD-n corresponds to the ground connection in the connected state and the maximum negative voltages Vb and Vt.

[0049] In one embodiment of the present invention, the average deflection velocity vn is defined by dividing the position difference between ADn and AD-n by the rise time t required to reach the respective maximum deflection state from the time the respective voltages are switched on, and preferably vn is between 0.025 μm / μs and 100 μm / μs, and more preferably between 0.2 μm / μs and 37.5 μm / μs.

[0050] In one embodiment of the present invention, the maximum voltages Vbn and Vtn are between 20 and 250 volts, and more preferably between 40 and 200 volts.

[0051] In one embodiment of the present invention, ET is defined as the downward deflection ejection threshold at which the material is ejected from the print head, preferably ET is between 0.3 μm and 40 μm, and more preferably between 1 μm and 30 μm.

[0052] In one embodiment of the present invention, PT is defined as the refill threshold of the printhead in upward deflection where the ejection region is primed with the material being ejected, preferably PT is between 0.3 μm and 40 μm, and more preferably between 1 μm and 30 μm.

[0053] In one embodiment of the present invention, the first and second voltages and the ground connection state are selected so that the actuator unit maintains a deflection state above ET for a period of 0.2 to 75 microseconds.

[0054] In one embodiment of the present invention, the first and second voltages and the ground connection state are selected so that the actuator unit maintains a deflection state above PT for a period of 0.2 to 70 microseconds.

[0055] In one embodiment of the present invention, the first and second voltages and the ground connection state are selected so that the actuator unit is deflected at an average deflection speed between 0.025 μm / μs and 100 μm / μs.

[0056] In one embodiment of the present invention, the first and second voltages and the ground connection state are selected such that the displacement of the actuator is less than the speed of sound of the liquid material ejected from the print head. [Modes for carrying out the invention]

[0057] Printhead structure

[0058] When referring to the printhead, the following directional definitions apply: Actuator movement is generally defined as upward and downward, and ejection is associated with downward movement.

[0059] The vertical direction of the print head is defined perpendicular to the upward and downward directions, and this is also the smaller dimension of the actuator and the larger dimension of the print head. Consequently, the remaining direction is referred to as the vertical direction of the actuator, which is the larger dimension of the actuator and the smaller dimension of the print head.

[0060] The aforementioned directions are defined merely to improve the comprehensibility of this explanation, and directions and / or dimensions can be specified using any other coordinate system suitable for describing 3D space, particularly in the attached drawings.

[0061] In one embodiment of the present invention, the print head comprises a plurality of material ejection units. Each material ejection unit comprises at least one actuator unit. The material ejection units are preferably arranged in parallel, i.e., each actuator unit is arranged parallel to the others in the longitudinal direction of the print head. Preferably, the material ejection units are formed in a common housing, i.e., the print head housing.

[0062] In one embodiment of the present invention, the printhead housing also includes, or partially includes, electromechanical and / or fluid components of one or more material ejection units.

[0063] In one embodiment of the present invention, two or more actuator units form an actuator block. Preferably, one or more actuator blocks form an actuator assembly. The actuator assembly, a corresponding fluid structure within the printhead housing, and corresponding electrical and fluid connection means form a printhead.

[0064] A general embodiment of the actuator unit according to the present invention is shown in Figure 6. Multiple, preferably 32, of the actuator units form an actuator block as shown in Figure 8. The connection of multiple actuator blocks forms an actuator assembly as shown in Figure 9. A generally linear arrangement of the actuator units and / or actuator blocks is preferred, but other arrangements such as zigzag, double-row, or multi-row arrangements are equally suitable and may even form a preferred specific embodiment depending on the application.

[0065] The following describes basic features with reference to general embodiments and specific features with reference to specific embodiments. Unless otherwise indicated or obvious to those skilled in the art, all features may be included in all embodiments.

[0066] In a preferred embodiment of the present invention, one actuator block includes 4 to 256, more preferably 32, actuator units. In a preferred embodiment of the present invention, one actuator assembly includes 1 to 16, more preferably 3, actuator blocks.

[0067] In one embodiment of the present invention, the printhead housing includes a space for housing an actuator assembly. The printhead housing may further include a fluid structure corresponding to the actuator assembly.

[0068] In one embodiment of the present invention, the fluid structure includes a material dispensing structure having a dispensing region for each actuator unit, which is suitable for dispensing material based on a temporary pressurization induced in the material within the dispensing region by each actuator unit.

[0069] The fluid structure further includes a material transport structure for transporting the discharged material to and from each material discharge region.

[0070] In one embodiment of the present invention, the material transport structure includes one or more material inflow channels for transporting material from an inflow connector to one or more material discharge regions.

[0071] In one embodiment of the present invention, the material inlet channel includes at least one joint at one or more locations in the width direction that connects at least one of the inlet channel and the outlet channel to one or more inlet and / or outlet connectors, respectively.

[0072] The joint is a fluid conduit section that connects one or more material inflow connectors to the material inflow channel at a point other than the endpoint of the material inflow channel, thereby causing a branching of the material flow direction from the joint to the inflow channel.

[0073] Furthermore, the joint is a fluid conduit section that connects one or more material outflow connectors to the material outflow channel at a point other than the endpoint of the material outflow channel, thereby causing multiple material flow directions from the outflow channel to converge towards the joint.

[0074] In one embodiment of the present invention, the material transport structure includes one or more material discharge channels for transporting material from one or more material discharge regions to a discharge connector.

[0075] In an alternative embodiment of the present invention, a plurality of material inflow connectors may be connected to an inflow channel, where the inflow channel includes one or more joints, preferably two or more joints, which are arranged at equal intervals along the length of the material inflow channel and connect the inflow channel to one inflow connector each.

[0076] In an alternative embodiment of the present invention, a plurality of material discharge connectors may be connected to a discharge channel, where the discharge channel includes one or more joints, preferably two or more joints, which are arranged at equal intervals along the length of the material discharge channel and connect the discharge channel to one discharge connector each.

[0077] In an alternative embodiment of the present invention, a plurality of material discharge connectors are connected to an inflow channel, where the discharge channel preferably includes connected discharge connectors arranged at equal intervals along the length of the material inflow channel.

[0078] In an alternative embodiment of the present invention, the flow direction of the liquid material in the conduit structure between the inlet connector and the outlet connector may be reversed.

[0079] In one embodiment of the present invention, the material dispensing region is formed in the material dispensing channel.

[0080] In one embodiment of the present invention, the material transport structure is located below the actuator assembly and above the nozzle plate. The material transport structure has openings through which each extension member of the actuator assembly reaches the fluid structure and communicates with its respective material discharge area.

[0081] In a preferred embodiment of the present invention, the print head housing is formed by stacking two or more plate-like elements on top of each other, thereby defining the space and / or fluid structure. The plate-like elements may have one or more recesses and / or notches for defining the space and fluid structure when attached to each other.

[0082] In other words, the central housing component may be formed by two or more adjacent plate-like structures having complex shapes that define the cross-section of the main housing structure.

[0083] The lamination of the plate-like elements enables a simplified manufacturing process for printhead components using one or more methods, such as etching, laser ablation, disk cutting, injection molding, or milling. This simplified manufacturing process allows for the production of a multilayer conduit network that enables proper fluid distribution.

[0084] Furthermore, by enabling each component of the fluid plate to be referenced along the xy plane during the manufacturing process, alignment is enhanced during the process of joining or bonding the components by adhesive or welding.

[0085] For the sake of easier understanding of this specification, the discharge unit is hereby assumed to include an actuator unit, a portion of the lower plate stack corresponding to the width of the material discharge channel, and two halves of the separating sidewall of the channel formed in the fluid plate, as shown in Figures 3a and 3b.

[0086] Specifically, the discharge unit may include a segment of the full channel width, two halves of the sidewall width of the elements present in the spacing element, a nozzle plate segment, a membrane element segment, a lower intermediate plate segment, a main fluid plate segment, a heating plate segment, and a corresponding actuator unit.

[0087] However, since the ejection unit may not be a physically separate element of the print head, the ejection unit may be defined in any other way, as long as the same structure as the print head can be obtained by connecting the ejection units.

[0088] Electromechanical Actuator Design

[0089] Scalable printhead designs are necessary to improve the efficiency and / or quality of the printing process. This means allowing multiple material ejection units to be positioned relatively close to each other within the printhead and / or within a single printhead housing.

[0090] The preferred spacing between the nozzle openings 201 of the material ejection unit is 2 mm to 0.2 mm, more preferably 1.5 mm to 0.5 mm. The preferred number of material ejection units in the print head is 32 to 256, more preferably 96.

[0091] The first core concept of the present invention is to provide a simplified mechanical and electrical actuator design. This enables efficient coupling of actuator units within the print head, thus resulting in reduced spacing and a print head with high native resolution.

[0092] A second core concept of the present invention is to provide a simplified fluid design for a material circulation system. This enables efficient coupling of actuator units within the print head, thus resulting in reduced spacing and a print head with higher native resolution.

[0093] A third core concept of the present invention is to provide a simplified driving method for a printhead. This enables efficient droplet ejection, and therefore results in a printhead with reduced spacing and higher native resolution.

[0094] In the above, the term "higher native resolution" is relative to other high-viscosity systems. High DPI is typically considered to be above 800 DPI. This invention operates at 20 DPI, which is an improvement over the typical 10 DPI obtained from the aforementioned other high-viscosity systems.

[0095] In embodiments of the present invention, the actuator is formed as a cantilever actuator having a stiffening element also called a spacing element.

[0096] The stiffening element is connected to the upper or lower surface of the piezoelectric element. The connection provides the piezoelectric element with an elastic mechanism for converting the d31 deformation into substantially orthogonal deformations via differential expansion between the piezoelectric element and the stiffening element at the connection boundary.

[0097] The stiffening elements further provide spacing between two or more piezoelectric elements bonded to the upper and lower surfaces, increasing the width of the stack of stiffening elements rigidly bonded to the stack, and therefore increasing its rigidity. In a preferred invention, the stiffening elements are nonconductive and may be composed of one or more of the following materials: glass fiber material, carbon fiber material, metal oxide material, composite material, or ceramic material.

[0098] The electrical connection of the actuator is configured to easily adjust the displacement of the actuator by using a switch that connects the stiffening element to ground via a grounding wire, thereby displacing the actuator through the extension and contraction of a piezoelectric element having a voltage potential that generates an electric field from the piezoelectric electrode to the stiffening element.

[0099] The electrodes discussed in this disclosure as being formed on a piezoelectric element preferably cover the upper and / or lower surface of the piezoelectric element and are preferably formed of a conductive thin film.

[0100] The displacement of the actuator is driven by positive and negative voltages, preferably applied simultaneously to the upper and lower piezoelectric electrodes. The difference in the direction of displacement of the piezoelectric elements for the same voltage value applied to the upper and lower piezoelectric electrodes is achieved through the selection of the polarization of the upper and lower piezoelectric elements, which will hereafter be referred to as the lower piezoelectric element.

[0101] The polarizations are selected to be in the same direction, preferably downward, such that the electric field applied to one piezoelectric element is substantially parallel to its polarization, while the electric field applied to the other piezoelectric element is substantially antiparallel to its polarization.

[0102] While the values ​​of one or more high-voltage signals can be switched between multiple states, the operating speed can be temporally shaped, or shaping, by independently switching the grounding switch between the open and closed states.

[0103] This temporal formation leads to improved adaptability to high-viscosity materials with complex rheologies. Furthermore, it allows for compensation of individual nozzle performance without the use of complex drive electronics such as FPGAs. In particular, the present invention does not require highly complex drive electronics and instead enables multi-pulse-based control using a high-speed switching ground gate.

[0104] Temporal shaping of actuator displacement, and preferably large displacement amplitude, are important factors for achieving high-viscosity dispensing.

[0105] In the print head according to the present invention, the pumping displacement is maintained for a longer period than is typical in some other print heads, due to a longer temporal vertical displacement following a variable speed, thereby enabling the pressurization to be maintained for an extended period compared to the normal pressurization time in other print heads.

[0106] Furthermore, the extended pressurization of the liquid material, primarily in the subsonic range, leads to different droplet formation and droplet release of the liquid material on the underside of the nozzle.

[0107] Therefore, a short pressure front is generated, which preferably imparts a substantial portion of its energy at the liquid-gas interface of the meniscus, thereby causing the meniscus to expand, leading to droplet formation and discharge.

[0108] This allows the material to flow out of the nozzle and form droplets, while controlling the size and release point through waveform modulation and / or multiple operations.

[0109] The cantilever configuration according to the present invention allows for large displacements similar to conventional actuator designs, but with a much smaller footprint, for example, 4mm x 6mm x 1mm compared to 8mm x 10mm x 2mm for conventional designs. Furthermore, comparable results can sometimes be achieved with much lower voltages, such as ±150 volts instead of the conventional ±200 volts.

[0110] Furthermore, according to the present invention, highly reduced harmonic resonance can be obtained.

[0111] In embodiments of the present invention, the displacement of the actuator is still primarily vertical. However, due to the geometric shape of the actuator, radial displacement, and therefore substantially lateral displacement of the underside of the extension member, may be introduced.

[0112] With respect to the multi-actuator unit, the present invention enables a completely modular, infinitely expandable, and highly simplified manufacturing and bonding process.

[0113] fluid design

[0114] As described above, the actuator unit according to the present invention preferably includes a piezoelectric system having delicate electrical and / or mechanical components. Furthermore, a high voltage is used to actuate one or more piezoelectric elements of the piezoelectric system. Therefore, it is desirable that the liquid in the print head does not come into contact with the actuator assembly.

[0115] Furthermore, since the liquid is preferably heated to maintain a specific viscosity, excessive heat transfer from the liquid to the actuator and vice versa should be prevented. However, at the same time, efficient impulse transmission should also be maintained, which requires direct contact between the actuator assembly and the liquid.

[0116] The core concept of the present invention is to provide a membrane within the print head to separate the liquid from the actuator. Embodiments of the present invention relate to different variations and arrangements of the membrane.

[0117] In embodiments of the present invention, the film prevents the liquid material from coming into contact with the actuator, thereby reducing the need for coating the actuator components to prevent heat transfer and electrical short circuits.

[0118] Furthermore, the membrane according to the present invention enables more efficient pressurization of the pressurized region, i.e., the discharge region, and better refilling or priming, i.e., removal of captured gas from the pressurized region.

[0119] It should be noted that, in general, the term priming refers to the removal of the two-phase gas-liquid flow mode from the geometric shape by introducing a material into the geometric shape. More specifically, in the context of the present invention, the geometric shape may be an ejection region, also called a virtual chamber during a positive pressurization process, which is the pressurization of the pressurized region against ambient pressure or printhead back pressure when the actuator is not deflected from its neutral state.

[0120] The primed dispensing region must contain liquid material so that it is ready to be subjected to positive pressurization for the purpose of dispensing the material, and during the pressurization, only the motion of the gas-liquid two-phase interface in or near the corresponding nozzle opening is affected, which is also called meniscus formation.

[0121] In other words, the geometric shape must be completely wetted or filled with the liquid material so that no gas or vacuum pockets remain trapped within the primed geometric shape. In the case of gas trapping accumulation within the internal geometric shape, for example due to insufficient pressurization and gas ingestion, priming is necessary to ensure that performance degradation during the discharge process is avoided.

[0122] Refilling, particularly in the context of alternating states, refers to the repeated supply of material to a region where the material is discharged from the region and must be reintroduced without forming a two-phase flow mode confined within the refilling region, thereby preventing depletion of the discharge region.

[0123] In the context of the present invention, refilling generally occurs, at least partially, during the opposite and negative pressurization to the pressurization intended for dispensing the liquid material.

[0124] In embodiments of the present invention, a plurality of dispensing units are connected, their respective channels are connected, and they are optionally formed together with other auxiliary components such as connectors to membranes and material circulation systems. The material circulation system is configured to transport liquid material to and from each dispensing region.

[0125] The inlet and outlet channels are subject to positive and negative pressurization, respectively. This pressurization creates a differential pressure, which then generates a flow of material at a relative pressure that is lower than the ambient pressure but not low enough to draw gas bubbles through the nozzle opening, nor high enough to cause material to leak out of the nozzle opening.

[0126] In embodiments of the present invention, continuous pressure measurements may be performed in or near the highest and lowest pressurized regions within the material circulation system. Specifically, the measurements are performed in a section of the material conduit located between a pump that generates positive pressure and a print head, and / or in a section of the material conduit between a pump that generates negative pressure and a print head.

[0127] This allows for electrical adjustment to control the relative pressure of the pressurizing pump according to the reference material and its properties at each temperature. Each temperature may be measured and controlled via an internal heating plate inside the print head or via an additional heating element formed in the material supply system.

[0128] This ensures that a stable minimum velocity of material flow in the material circulation system is maintained in accordance with the aforementioned criteria.

[0129] In a first embodiment of the present invention, each fluid channel is formed to have a bypass structure with a constant cross-sectional area and a reduced cross-sectional area in order to provide equalization of the flow rate and pressure of the material present in the discharge channel during material recirculation. This configuration allows for uniform refilling of all present discharge areas.

[0130] In a second embodiment of the present invention, each fluid channel is formed with a stepwise decrease in the inflow channel volume in response to an increase in distance from the material inflow connector, and a corresponding increase in the outflow channel volume in response to an increase in distance to the material inflow connector.

[0131] In other words, the cross-sectional area of ​​each channel preferably changes gradually along the length. This improves the equalization of pressurization and flow rate of the liquid material present in the channel manifold between the inlet and outlet channels.

[0132] Nozzle plate displacement

[0133] In embodiments of the present invention, the nozzle plate is configured to displace during material discharge. Displacement may occur due to pressurization resulting from actuator displacement in the liquid material adjacent to the nozzle plate, thereby inducing a substantially parallel displacement of the section surrounding the nozzle opening in the discharge direction, and transferring displacement energy to the material present on the underside of the nozzle plate during the discharge process.

[0134] This can potentially improve dispensing performance by assisting in the release of fluid threads or pinch-off of the dispensing material, especially at very high viscosities or with materials having very high viscoelastic properties. [Brief explanation of the drawing]

[0135] [Figure 1] This figure shows a print head according to one embodiment of the present invention from an isometric projection angle viewpoint. [Figure 2] This figure shows a print head according to one embodiment of the present invention, viewed from an isometric angle. [Figure 3a] This is a cross-sectional view of a print head according to one embodiment of the present invention, cut along the direction of the actuator. [Figure 3b] This is a cross-sectional view of a print head according to an alternative embodiment of the present invention, cut along the direction of the actuator. [Figure 4] This is a bottom view of a print head according to one embodiment of the present invention, with the fluid plate in the open position. [Figure 5a] This is a bottom view of a print head according to one embodiment of the present invention, with spacing elements present. [Figure 5b]This is a bottom view of a print head according to one embodiment of the present invention, showing a state in which spacing elements are present and the recessed channel structure of the fluid plate is indicated by a dashed line. [Figure 6] This is an oblique isometric view of a cross-section of a print head according to one embodiment of the present invention, cut along the length direction of the actuator. [Figure 7] This is a cross-sectional view of an actuator unit relating to one embodiment of the present invention. [Figure 7a] This figure shows the layered structure of an actuator unit according to one embodiment of the present invention. [Figure 7b] This figure shows the drive signal applied to an actuator unit according to one embodiment of the present invention and the time change of the corresponding actuator displacement. [Figure 8] This figure shows an actuator block according to one embodiment of the present invention from an isometric projection angle viewpoint. [Figure 9] This figure shows an actuator block assembly according to one embodiment of the present invention from an isometric projection angle viewpoint. [Figure 10a] This is a schematic side view of a print head according to the first embodiment of the present invention, with the extension member in the neutral position. [Figure 10b] This is a schematic side view of a print head according to the first embodiment of the present invention, showing the extension member in a bent position. [Figure 11a] This is a schematic side view of a print head according to a second embodiment of the present invention. [Figure 11b] This figure shows a print head according to a second embodiment of the present invention, viewed from an isometric angle. [Figure 12a] This is a schematic side view of a print head according to the first embodiment of the present invention, showing the extension member in a bent position. [Figure 12b] This is a schematic side view of a print head according to the first embodiment of the present invention, showing the extension member in a bent position. [Figure 13a] This figure shows a print head according to a third embodiment of the present invention, viewed from an isometric angle. [Figure 13b]This is a schematic side view of a print head according to a third embodiment of the present invention. [Figure 14] This is a cross-sectional view of a print head according to a fourth embodiment of the present invention. [Figure 15] This is a cross-sectional view of a print head according to a sixth embodiment of the present invention. [Figure 16a] This figure shows a print head according to the seventh embodiment of the present invention, viewed from an isometric angle. [Figure 16b] This is a cross-sectional view of a print head according to a seventh embodiment of the present invention.

[0136] Embodiments of the present invention are described below. It should be noted that, unless explicitly stated otherwise or obvious to those skilled in the art, some aspects of the embodiments described may also be found in some other embodiments. However, for the sake of clarity, each aspect is described in detail only when first mentioned, and repeated descriptions of the same aspect are omitted.

[0137] Figure 1 shows a print head according to one embodiment of the present invention from an isometric angle view. The print head comprises a housing, a fluid connector for inputting and removing liquid material, a vacuum connector, and an electrical connector for providing electrical signals to the actuator unit of the actuator assembly within the housing.

[0138] As detailed above, in a preferred embodiment of the present invention, the print head is formed by different plate-like elements stacked vertically, i.e., along the ejection direction of the print head. This design allows for an improved assembly process because each plate-like element can be referenced independently.

[0139] In Figure 1, the print head comprises a main fluid plate 107 and a case element 106. Furthermore, the print head includes an electrical connector 102, a material inlet connector 103, a material outlet connector 104, a first vacuum connector 111, and a second vacuum connector 112.

[0140] The electrical connector 102, material inlet connector 103, material outlet connector 104, and material inlet connector 103 and material outlet connector 104 may be provided protruding upward from the upper surface of the case element 106. The structural and functional interrelationships of the above components will be described below.

[0141] Figure 2 shows a print head according to one embodiment of the present invention from an isometric angle view. Below the main fluid plate 107, as shown in Figure 1, a spacing element 202 is provided. Below the spacing element 202, a nozzle plate 109 is provided.

[0142] As detailed in the enlarged section of Figure 2, the nozzle plate 109 is provided with one or more nozzle openings or ejection openings 201.

[0143] Figures 3a and 3b show cross-sectional views of a print head according to one embodiment of the present invention, cut along the direction of the actuator.

[0144] Referring to Figures 1 and 2, the print head comprises an electrical connector 102, a main case 106, an upper PCB (printed circuit board) plate 502, an intermediate PCB plate 503, a lower PCB plate 504, a second vacuum connector 112, a heating plate 207, a main fluid plate 107, an actuator 301, an inlet channel 601, an outlet channel 602, a material ejection channel 603, a membrane element 203, a spacing element 202, a nozzle plate 109, and an actuator 401.

[0145] Please note that the first vacuum connector 111, the material inlet connector 103, and the material outlet connector 104, as well as their respective conduit connections, are not shown in Figure 3a.

[0146] An actuator 301 having an extension member 401 is provided inside the print head, preferably in a space defined by the main fluid plate 107 and the case element 106. The extension member 401 extends from the actuator 301 to or into the material present in the main fluid plate 107. The longitudinal actuator has one fixed end portion fixed to the housing. Furthermore, the longitudinal actuator has one free end portion that can bend up and down and thus actuate the extension member.

[0147] As described above, additionally or alternatively, the upper PCB plate 502 may be provided together with the intermediate PCB plate 503, the lower PCB plate 504, and the main fluid plate 107 to surround the actuator 301.

[0148] The upper PCB plate 502, the intermediate PCB plate 503, and the lower PCB plate 504 preferably include conductive connection elements that allow electrical signals to pass from the electrical connector 102 to the actuator 301, the heating plate connection element 501, and / or to further elements inside the print head.

[0149] The main fluid plate 107 may also include one or more fluid connector elements for supplying and removing liquid material from the print head.

[0150] Within the main fluid plate 107, several spaces for liquid are provided, preferably defined by recesses within the main fluid plate 107.

[0151] In detail, the main fluid plate 107 includes a fluid inlet channel 601, a fluid outlet channel 602, and one or more material ejection channels 603. Each inlet / outlet channel extends along the underside of the main fluid plate 107, perpendicular to the ejection direction and substantially parallel to the actuator connection direction; that is, along the length of the print head.

[0152] In one embodiment of the present invention, the extension member 401 is positioned on the free end portion of the lower surface of the actuator in order to achieve maximum deflection.

[0153] In an alternative embodiment of the present invention, as shown in Figures 3b and 6, the extension member 401 is formed at a predetermined distance from the free end of the actuator, and an additional reference element 403 is positioned between the extension member 401 and the free end.

[0154] More generally, at least one additional reference element 403 is provided to define the position of the extension member relative to the end portion of the actuator. The reference element is configured to allow for simplified manufacturing.

[0155] A spacing element 202 is provided below the main fluid plate 107. Above the spacing element 202, that is, between the spacing element 202 and the main fluid plate 107, a membrane element 203 is provided and configured to connect to the central surface of the main fluid plate 107.

[0156] The main fluid plate 107 preferably includes spaces that form each through portion, where each extension member is positioned to reach out from each actuator 301 toward or into the ejection channel 603.

[0157] The membrane element 203 is further connected to the surface of the main fluid plate that defines the lower surface of the extension member 401 and the upper surface of the ejection channel 203.

[0158] The membrane element 203 is configured to separate the penetration portion of the fluid plate from the channel formed by the spacing element, thereby preventing the liquid material present in the ejection channel 603 from entering the penetration portion.

[0159] Figure 3b shows a cross-sectional view of a printhead according to one embodiment of the present invention, cut along the direction of the actuator having a reference element 403. In detail, the drawing shows an inlet connector 103, an outlet connector 104, an inlet channel 601, and an outlet channel 602. As described above, the printhead further includes an upper reference element 505, a middle reference element 506, and a lower reference element 507.

[0160] The inlet channel 601 is in fluid communication with the discharge channel 603 through the heating plate 207 (not shown in Figure 3b), preferably through one or more holes in the heating plate.

[0161] The outflow channel 602 is in fluid communication with the discharge channel 603 through the heating plate 207, preferably through one or more through holes or openings in the heating plate.

[0162] In one embodiment of the present invention, channel structures, also called conduits, and / or other elements of the fluid structure are manufactured by injection molding or laser ablation in a thermoplastic polyimide material or similar material to form the plate elements of the print head. Alternatively, the structures may be etched into a metal substrate to form the plate elements of the print head.

[0163] In other words, according to the general invention, the fluid plate 107 is provided with two separate first channels along the longitudinal direction of the print head. A membrane and a heating plate are optionally provided below the main fluid plate. Below the main fluid plate and the heating plate, a spacing element is provided which has a plurality of second channels, also called material discharge channels.

[0164] The second channel is preferably formed through through holes and / or recesses within the spacing element 202. The second channel is substantially perpendicular to the first channel. The second channel is located at a position corresponding to an extension member of the printhead actuator unit, extending through the pass-through portion of the main fluid plate.

[0165] Below the spacing element, a nozzle plate is provided which includes a plurality of nozzle openings 201 that are positionally corresponding to the second channel.

[0166] One of the first channels is suitable for material inflow; that is, it is connected to an inflow connector and / or formed for material transport in the inflow direction.

[0167] One of the other channels of the first channel is suitable for material outflow; that is, it is connected to an outflow connector and / or formed for material transport in the outflow direction.

[0168] The second channel is suitable for connecting two first channels. The first and second channels are fluid-connected, preferably through an arbitrary heating plate. Fluid connection is preferably made through the respective holes in the heating plate.

[0169] In other words, the arrangement of the first and second channels forms a pressurized region. Furthermore, a discharge region is formed between the lower surface of the extension member and above the nozzle opening 201.

[0170] In the plate-like structure, channels may be formed as notches and / or recesses in each plate-like element, or a combination thereof. During assembly, each plate-like element can be referenced individually. Therefore, the material transport structure can be assembled more efficiently and accurately.

[0171] In one embodiment of the present invention, the preferred dimensions of the first channel, which is an inlet channel, are a width of 0.4 mm to 10 mm, a height of 0.4 mm to 4.2 mm, more preferably a width of 0.8 mm to 7 mm, a height of 0.5 mm to 3.8 mm, and a length at least longer than the length of the connected channel discharge manifold.

[0172] In an alternative embodiment, the dimensions of the cross-section of the first channel are changed, i.e., the channel is convex and perpendicular to the general flow direction and length of the first channel.

[0173] The aforementioned cross-sectional area has a ratio of 1 to 5 between its major axis and its corresponding minor axis, and an area of ​​0.16 mm². 2 ~42mm 2 , more preferably 0.4 mm 2 ~26.6mm 2 The length of the first channel is at least longer than the length of the 96-channel discharge manifold, i.e., at least 130 mm in addition to 20 mm of extra space for including one or more bypass structures around the channel discharge manifold.

[0174] In one embodiment of the present invention, the preferred dimensions of the first channel, which is an outflow channel, are a width of 0.4 mm to 10 mm, a height of 0.4 mm to 4.2 mm, more preferably a width of 0.8 mm to 7 mm, a height of 0.5 mm to 3.8 mm, and a length at least longer than the length of the connected channel discharge manifold.

[0175] In other words, for a 96 nozzle manifold, it is at least 130 mm in length, plus an additional 20 mm of space to include one or more bypass structures around the channel discharge manifold.

[0176] In a preferred embodiment of the present invention, the dimensions of the second channel are such that the cross-sectional area is perpendicular to the general flow direction and length of the second channel.

[0177] The aforementioned cross-sectional area has a ratio of 1 to 10 between its major axis and its corresponding minor axis, and the cross-sectional area is 0.01 mm². 2 ~0.45mm 2 , more preferably 0.08 mm 2 ~0.3mm 2 The length of the first channel is at least longer than the length of the connected channel discharge manifold.

[0178] In one embodiment of the present invention, the preferred dimensions of the second channel (i.e., the manifold channel or the discharge channel) are a width of 0.7 mm to 1.2 mm, a height of 0.1 mm to 0.35 mm, more preferably a width of 0.8 mm to 1.3 mm, a height of 0.14 mm to 0.25 mm, and a length of at least 3.4 mm.

[0179] In an alternative embodiment of the present invention, the second channel includes a substantially parallel and narrower third channel provided with and / or cut with a recess in the central portion of the second channel. The third channel has a smaller width than the second channel, a width of 0.1 mm to 1 mm, a height of 0.01 mm to 0.09 mm, more preferably a width of 0.2 mm to 0.8 mm, and a height of 0.02 mm to 0.07 mm. The channel width may vary within the above values along the longitudinal direction of the third channel.

[0180] As described above, in one embodiment of the present invention, each fluid channel is formed with a gradual decrease in the inflow channel volume corresponding to an increase in the distance from the material inflow connector and a corresponding increase in the outflow channel volume corresponding to an increase in the distance to the material inflow connector.

[0181] That is, the cross-section of each channel gradually changes. This enables the equalized pressurization of the liquid material present in the channel manifold between the inflow channel and the outflow channel.

[0182] In a preferred embodiment of the present invention, the inflow channel has dimensions of a height of 1.9 mm and a width of 6 mm along the length of the inflow channel.

[0183] In an alternative embodiment of the present invention, the dimensions of the first channel are such that the cross-sectional area is convex and orthogonal to the general flow direction of the first channel and its length. The cross-sectional area has a ratio of the long axis to the corresponding short axis of 1 to 5, and the area is 10 mm 2 ~16 mm 2 along the length of the inflow channel.

[0184] In an alternative embodiment of the present invention, the inflow channel has dimensions of 1.9 mm in height and 6 mm in width at the inflow connector of the print head, and these dimensions are reduced to 0.19 mm in height and 1 mm in width at the opposite end.

[0185] Alternatively, in an alternative embodiment of the present invention, the dimensions of the first channel are such that the cross-sectional area is convex and perpendicular to the general flow direction and length of the first channel. The relationship between the major axis and the corresponding minor axis of the cross-sectional area is 1 to 5, and the area at the inlet end of the print head is 10 mm². 2 ~16mm 2 The area at the opposite end is 0.1 mm². 2 ~0.2mm 2 It decreases to [a certain value].

[0186] Accordingly, the dimensions of the outflow channel at the printhead's inflow end, which are 0.18 mm high and 0.8 mm wide, are increased to 3.7 mm high and 3.7 mm wide at the opposite end.

[0187] Alternatively, the dimensions of the second channel are such that the cross-sectional area is convex and perpendicular to the general flow direction and length of the second channel. The relationship between the major axis and the corresponding minor axis of the cross-sectional area is 1 to 5, and the area at the inlet end of the print head is 0.1 mm². 2 ~0.2mm 2 And the area at the opposite end is 10 mm² 2 ~16mm 2 It increases to [a certain value].

[0188] The above example relates to a rectangular cross-section. However, other cross-sectional shapes are possible in other embodiments of the present invention.

[0189] In other words, in a preferred embodiment of the present invention, the cross-sectional size of the inflow channel decreases by approximately 1% from the first end to the second end, while the cross-sectional size of the outflow end increases accordingly.

[0190] Alternatively, in a preferred embodiment of the present invention, the cross-sectional size of the inflow channel decreases to approximately 1 / x from the first end to the second end, where x is the number of channels present along the length of the channel manifold. The cross-sectional size of the outflow end increases accordingly.

[0191] In a preferred embodiment of the present invention, the reduction in cross-sectional area is non-uniform with respect to the long and short axes along the general flow direction axis. Specifically, the height is reduced to about 4.8%, and the width is reduced to about 21%.

[0192] The decrease or increase is preferably carried out in a substantially linear manner.

[0193] In one embodiment of the present invention, the heating plate 207 may be located below the fluid plate 107 and above the spacing element 202. Alternatively, the membrane element 203 further includes a heating portion embedded therein.

[0194] The heating plate is connected to the upper plate or upper PCB via a heating plate connecting element 501. Heat dissipation is controlled via pulse width modulation of the voltage. In an alternative embodiment of the present invention, heat dissipation is controlled via a variable voltage. The heating plate is configured to transfer heat primarily to the liquid material present in the conduits of the fluid plate 107 and the spacing element 202.

[0195] The actuator 301 includes one or more piezoelectric elements. The piezoelectric elements are connected to the electrical connector 102 via a flexible printed circuit board 501, or flex PCB.

[0196] This configuration allows for improved expandability based on the close proximity of the actuators. Therefore, it becomes possible to form pre-fabricated actuator blocks, and further, to connect these actuator blocks to obtain a variable-size actuator assembly for a variable printhead width.

[0197] Furthermore, this configuration allows for easy fastening of the actuator unit to the fluid plate and / or, in alternative embodiments of the present invention, to the retaining element, thereby fixing the actuator at a specific point for the purpose of having precise deformation of the non-fixed actuator portion.

[0198] This effectively achieves an improved and uniform displacement range for the extension member when the same electrical signal is applied.

[0199] Figure 4 shows the bottom surface of a print head according to one embodiment of the present invention, where the fluid plate 107 is visible. In other words, the lower surface of the fluid plate 107 is shown.

[0200] The fluid plate 107 includes a fluid inlet channel 601 and a fluid outlet channel 602. The inlet and outlet channels are connected to one of the inlet connection point 604 and the outlet connection point 605, respectively. The inlet and outlet channels are preferably formed as recesses within the fluid plate 107.

[0201] The inlet and outlet channels are preferably configured to allow the liquid material to flow through openings in the heating plate, spacing elements and / or nozzle plate, or other elements (not shown) fixed below the mean fluid plate 107. The geometry of the inlet and outlet channels may be optimized as described below.

[0202] In a preferred embodiment of the present invention, a membrane element 203 is provided below the generally central part of the fluid plate 107, and below the membrane, a spacing element 202 is provided for defining a portion of the fluid transport structure of the print head, including a pressurized area. Below the spacing element, a nozzle plate having a corresponding nozzle opening is provided.

[0203] In preferred embodiments, the film has a thickness of 7 μm to 100 μm, preferably 10 μm to 50 μm, and is manufactured from one or more of the following polymer materials: polyimide, PTFE, PFA, FEP, or ETFE.

[0204] In a preferred embodiment of the present invention, the inlet and outlet channels are connected via a discharge channel and one or more bypass sections 612 and 611 that allow material to flow directly from the inlet channel to the outlet channel. The bypass sections preferably have a cross-sectional area equal to or smaller than that of the inlet and outlet channels.

[0205] Furthermore, the fluid plate 107 includes an extension member through-opening 206 configured to accommodate an extension member, or at least the end 606 of an extension member of a corresponding actuator unit positioned above the fluid plate 107.

[0206] Figure 5a shows the bottom surface of a print head according to one embodiment of the present invention, where a spacing element 202 is present, and the bottom surface that contacts the film and the pass-through portion that contacts the film are indicated by dashed lines.

[0207] In one embodiment of the present invention, the membrane is coupled to the region of the main fluid plate 107 surrounding the pass-through portion where the extension member is located, and to the lower surface of the extension member. The membrane is elastic and thereby undergoes partial displacement within the region covering the pass-through portion when the extension member is operated by the actuator.

[0208] In one embodiment of the present invention, the lower surface of the membrane is connected to a lower intermediate plate 613, which is directly attached to the lower surface of an extension member and may have a different diameter or shape from the lower surface of the extension member. Displacement of the lower intermediate plate 613 via the extension member causes deformation of the membrane.

[0209] Optionally, the lower intermediate plate 613 may be used with a more efficient method for manufacturing the film, or with a molded film precisely bonded to the actuator unit. See Figure 11a.

[0210] In one embodiment of the present invention, the spacing element 202 is provided below the fluid plate 107. The spacing element 202 further includes recesses and / or through holes that define material discharge channels having a non-rectangular cross-sectional area.

[0211] In an alternative embodiment of the present invention, the spacing element 202 includes a through-hole defining a material discharge channel 603 below the membrane element 203, the defined material discharge channel having a rectangular cross-sectional area.

[0212] As described above, the material discharge channel 603 of each discharge unit is in fluid communication with the inflow and outflow channels, respectively, preferably through holes in the heating plate 207. The shape of the membrane may be optimized as detailed below.

[0213] Figure 5b shows the lower surface of a print head according to one embodiment of the present invention, in which a spacing element 202 is present, the recessed channel structure of the fluid plate 107 is shown by a dashed line, and the recessed channel structure and through-holes located within the spacing element 202 are shown.

[0214] As described above, a spacing element 202, a membrane element 203, and a fluid plate 107 are provided above the membrane element 203. In the fluid plate 107, the inlet channel 601 and the outlet channel 602 are formed in the longitudinal direction of the print head, i.e., in the connection direction of the actuator assembly.

[0215] The applicant recognized that the flow velocity in the discharge channel 603 is related to the back pressure at the nozzle opening. Therefore, a compromise is needed between the ideal flow rate and pressure fluctuations.

[0216] To overcome the above problems, one or more bypass sections are provided between the inlet and outlet channels. The bypass sections allow the flow rate and back pressure to be controlled independently of each other. That is, a uniform back pressure can be obtained for all nozzle openings while increasing the flow rate.

[0217] In a preferred embodiment, the bypass section may have a height dimension of 0.18 mm to 2 mm, a width dimension of 0.8 mm to 6 mm, and a length dimension of 6 mm to 20.3 mm.

[0218] A first bypass section 611 is shown, passing around the discharge channel manifold and connecting the inflow and outflow channels. A second bypass section (not shown) is preferably arranged symmetrically with respect to the first bypass section.

[0219] In the spacing element 202 located below the membrane element 203, a plurality of discharge channels 603 are provided corresponding to each discharge unit. The discharge channels 603 are provided perpendicular to the channels of the fluid plate 107.

[0220] In other words, each discharge channel 603 connects the inlet channel 601 and the outlet channel 602 at the location of the respective discharge unit. Specifically, the discharge channels 603 are located at a position corresponding to the lower part of the extension member 606 that passes through the fluid plate, or they contact the membrane element 203 at the extension member opening 207 of the fluid plate 107.

[0221] As described above, at the intersection of one of the inflow and outflow channels and the discharge channel 603, the channels are in liquid communication, and preferably a heating plate through-opening is provided for liquid communication between each channel and the discharge channel 603.

[0222] Figure 6 shows an oblique isometric view of a cross-section of a printhead section according to one embodiment of the present invention, cut along the longitudinal direction of the actuator.

[0223] In other words, a segmented cross-section of the printhead is shown, which is essentially a three-dimensional interpretation of Figure 3, illustrating the three-dimensional structure formed by stacking different plates of the printhead.

[0224] As described above, the sections shown in Figure 6 can be linked together any number of times to scale the size of the print head, i.e., the number of ejection units.

[0225] In a preferred embodiment of the present invention, the plate element has one or more of the following thicknesses: - Typical thickness of the plate-like portion of the main fluid plate 107: 1 mm to 6 mm, preferably 1.5 mm to 5 mm, most preferably 2.5 mm to 4 mm. - Membrane element 203: 0.005 mm to 0.07 mm, preferably 0.008 mm to 0.05 mm, most preferably 0.01 mm to 0.025 mm. - Spacing element 202: 0.1mm to 0.25mm, preferably 0.12mm to 0.22mm, most preferably 0.15mm to 0.21mm. - Nozzle plate 109: 0.01mm to 0.3mm, preferably 0.025mm to 0.1mm, most preferably 0.04mm to 0.08mm.

[0226] The fluid channel has a width of 2 mm to 8.2 mm, more preferably 0.8 mm to 7.1 mm, and most preferably 3.8 mm to 6.5 mm.

[0227] Figure 6 further shows how the discharge channel 603 is formed below the membrane element 203 and how the nozzle opening 201 and the extension member are aligned.

[0228] Figure 7 shows a cross-sectional view of an actuator unit according to one embodiment of the present invention and illustrates the electrical signals in the actuator design according to one embodiment of the present invention. Each actuator unit includes a rigidifying element 304, an upper piezoelectric element 302, and a lower piezoelectric element 303, which are sandwiched together to form a piezoelectric stack, also known as a trimorph actuator 301.

[0229] In a preferred embodiment of the present invention, the upper and lower piezoelectric elements are bonded to the stiffening element via one or more different adhesives, preferably epoxy adhesives. Furthermore, the piezoelectric elements may be bonded to the stiffening element via direct thermal welding or ultrasonic welding.

[0230] Each piezoelectric element is electrically connected to a high-voltage line 514 and a ground line 516 for the purpose of transmitting electrical signals to and from the piezoelectric element.

[0231] Figure 7a shows the layered structure of an actuator according to one embodiment of the present invention. More specifically, Figure 7a shows the surface of the actuator structure.

[0232] In a preferred embodiment of the present invention, the upper surfaces J of each upper piezoelectric element are connected to a high-voltage drive signal via a conductive structure located on or inside the middle PCB plate 503, and more preferably to an electrical connector 102 via a conductive structure located on or inside the upper PCB plate 502, thereby enabling the connection of a drive signal source for supplying high voltage to the upper surfaces of the upper piezoelectric elements.

[0233] The conductive structure or electrode is preferably a thin metal film having one or more compositions from copper-nickel alloy, copper, gold, silver, nickel, rhodium, or copper-zinc alloy. The thin film is coated and / or structured via one of sputtering, physical vapor deposition, atomic layer deposition, spin coating, etching, or inkjet.

[0234] In a preferred embodiment of the present invention, the lower surface (K) of each lower piezoelectric element is connected to a high-voltage drive signal via a conductive structure located on or inside the lower PCB plate 504, and preferably further connected to an electrical connector 102 via a conductive structure located on or inside the lower reference element 507, the middle reference element 506, the upper reference element 505, the middle PCB plate 503, and the upper PCB plate 502, thereby enabling the connection of a drive signal source for supplying high voltage to the lower surface of the lower piezoelectric element.

[0235] In one embodiment of the present invention, the upper surface J of the upper piezoelectric element is connected to a common high-voltage drive signal. The lower surface C of the upper piezoelectric element is connected to ground.

[0236] In one embodiment of the present invention, the lower surface K of the lower piezoelectric element is connected to a common high-voltage drive signal. The upper surface A of the lower piezoelectric element is connected to ground.

[0237] The length dimension of the piezoelectric element, i.e., the longest dimension, is preferably 5 mm to 13 mm, more preferably 6 mm to 12 mm, and most preferably 9 mm to 11 mm. The width dimension is preferably 0.5 mm to 2 mm, more preferably 0.8 mm to 1.2 mm, and most preferably 1 mm.

[0238] In a preferred embodiment of the present invention, the thickness is preferably 0.05 mm to 0.5 mm, more preferably 0.1 mm to 0.3 mm, and most preferably 0.13 mm to 0.25 mm.

[0239] The preferred dimensions of the rigidifying element are substantially the same in length and width, but with a length at least 0.1 mm shorter on one side than that of the piezoelectric element.

[0240] In a preferred embodiment of the present invention, the thickness of the rigidifying element is preferably 0.1 mm to 0.7 mm, more preferably 0.2 mm to 0.6 mm, and most preferably 0.3 mm to 0.5 mm.

[0241] Piezoelectric elements have directional residual polarization along the stacking direction and are generally polarized in such a way that when a positive voltage is applied via a high-voltage line, the difference in the resulting lateral deformation between the upper and lower piezoelectric elements causes a downward deflection of the actuator.

[0242] There are two common modes of piezoelectric energy operation. In d33 mode, the applied stress and applied voltage are in the same direction, while in d31 mode, the stress is applied axially, but the voltage is applied perpendicularly.

[0243] In a preferred embodiment of the present invention, the deflection of the actuator is caused by the differential lateral d31 deformation of the piezoelectric elements present in the actuator, which results in a substantially orthogonal deflection of the actuator with respect to the longitudinal direction of the actuator, via differential compliant deformation of the stiffening elements caused by the lateral deformation of each coupled piezoelectric element. When a negative voltage is applied via a high-voltage line, a reverse actuator deflection is induced.

[0244] In a preferred embodiment of the present invention, the voltages provided by the first and second high-voltage lines are the same value.

[0245] In an alternative embodiment of the present invention, the piezoelectric elements have directional residual polarization along the stacking direction and are generally polarized in such a manner that when a negative voltage is applied via a high-voltage line, the resulting difference in lateral deformation between the upper and lower piezoelectric elements causes a downward deflection of the actuator.

[0246] In an alternative embodiment of the present invention, different voltages are applied to a first high-voltage line and a second high-voltage line to cause a controlled differential between the deflections of the piezoelectric element.

[0247] In an alternative embodiment of the present invention, the piezoelectric element has a residual polarization in the opposite or different direction, and a voltage can be independently applied to cause controlled actuator deflection.

[0248] In a preferred embodiment of the present invention, the transient polarization of the piezoelectric element, i.e., the polarization generated by the applied voltage, is generated through electrical connections on the upper and lower surfaces of the upper and lower piezoelectric elements. The upper side of the upper piezoelectric element is referred to as the J surface in Figure 7a.

[0249] The surface is preferably coated with a thin conductive metal film, in other words, an electrode. The film is applied entirely or selectively via one of the following methods: sputtering, physical vapor deposition, atomic layer deposition, spin coating, etching, or inkjet. The surface preferably has a composition of one or more of the following: copper-nickel alloy, copper, gold, silver, nickel, rhodium, or copper-zinc alloy.

[0250] Preferably, the same film is applied to the upper and / or lower surfaces of the upper and / or lower piezoelectric elements.

[0251] The drive signal may be provided by a suitable signal source not described in detail in this description.

[0252] In a preferred embodiment of the present invention, the lower surface (M) of the upper piezoelectric element is connected to a conductive structure located within the middle reference element 506, which is further electrically connected to an electrical connector 102 via a conductive structure located on or within the upper reference element 505, the middle PCB plate 503, and the upper PCB plate 502, which provides a connection to ground.

[0253] In a preferred embodiment of the present invention, the upper surface (L) of the lower piezoelectric element is connected to a conductive structure located within the middle reference element 506, which is further electrically connected to an electrical connector 102 via a conductive structure located on or within the upper reference element 505, the middle PCB plate 503, and the upper PCB plate 502, which provides a connection to ground.

[0254] In a preferred embodiment of the present invention, each earth connection corresponds to an individual piezoelectric element, and each of the individual connections to earth is switchable from a connection to earth to a state forming an electrically disconnected conductive element.

[0255] In a preferred embodiment of the present invention, the connecting element may consist of a solder pad, a conductive trace, a contact pad, or a through-hole, enabling connection via soldering and / or electrical conductive coupling to a conductive element.

[0256] In an alternative embodiment of the present invention, the upper reference element 505, the middle reference element 506, and the lower reference element 507 may be replaced by a single element having a conductive structure and dimensions configured to enable the same functions as the individual reference elements.

[0257] As described above, the piezoelectric stack includes a rigidifying element 304, an upper piezoelectric element 302, and a lower piezoelectric element 303. An extension member 401 may be provided at one end of the piezoelectric stack, which may also be called a free end.

[0258] At the other end, electrical connections are provided via the central reference plate 506 through solder pads, contact pads, conductive traces, or through holes, enabling soldering or bonding via conductive elements.

[0259] At the central position, an upper clamping element 305 and a lower clamping element 306 are provided. These elements restrict the movement of the actuator at the central position, and only one end beyond the last contact point with either of them defines the free end of the piezoelectric stack and / or the free end of the actuator by moving in the direction of the extension member of the clamping element. The upper clamping element 305 is more preferably fixed to the upper PCB element 502, and the lower clamping element 306 is further fixed to the main fluid plate 107.

[0260] The upper reference element 505, the middle reference element 506, and the lower reference element 507 are used for spatial reference of the actuator stack, and surfaces (G and K) are formed on the underside of the lower piezoelectric element and the lower reference element, enabling precise coupling and positioning of the piezoelectric stack to the lower PCB plate 504. The lower PCB plate is further coupled to the main fluid plate 107, enabling precise positioning of the actuator.

[0261] Furthermore, surfaces (F and J) are formed on top of the upper piezoelectric element and upper reference element, enabling precise coupling of the piezoelectric stack and electrical connection of the piezoelectric stack to the upper PCB plate 505.

[0262] In a preferred embodiment of the present invention, the upper reference element and the lower reference element have substantially the same thickness as the respective upper and lower piezoelectric elements, and the middle reference element has the same thickness as the stiffening element.

[0263] The stiffening element preferably extends to the middle reference element, the element is a separate element, has a constant width corresponding to the width of the piezoelectric element, and preferably has a bonding length at least 1 mm longer than the length of the longest piezoelectric element.

[0264] In a preferred embodiment of the present invention, the upper and lower piezoelectric elements have similar lengths.

[0265] In an alternative embodiment of the present invention, the lower piezoelectric element has a length that is 100% to 134% of the length of the upper piezoelectric element, and the lengths of the corresponding reference elements are changed such that the total bonding length of the reference element and each piezoelectric element corresponds to a length that is approximately equal to the bonding length of the stiffening element and the middle reference element.

[0266] The stiffening element may be composed of a non-conductive material, that is, a glass fiber material, a carbon fiber material, a metal oxide material, a composite material or a ceramic material.

[0267] In an alternative embodiment of the present invention, the connection of the piezoelectric elements may be switched from the high voltage connection to the ground connection and vice versa, and a conductive stiffening element may be used, which may be composed of any of a conductive carbon fiber material, a metal material, or a non-conductive material having a conductive coating or film applied to the surface contacting the piezoelectric element and the middle reference element.

[0268] The lower surface of the upper piezoelectric element and the upper surface of the lower piezoelectric element are connected to a common ground line 516, which can be switched to be connected or disconnected from the ground, and are connected to the respective piezoelectric elements via the surfaces L and M formed in FIG. 7a.

[0269] In an alternative embodiment of the present invention, a conductive structure on or within the middle PCB plate 503 is in complete contact with the surface (J) and is coupled to the upper piezoelectric element 302 via a conductive adhesive or soldering.

[0270] Surface A is the corresponding interface between the lower piezoelectric element 303 and the stiffening element 304. This interface is also preferably non-conductively coupled via an epoxy adhesive or other non-conductive binder.

[0271] In an alternative embodiment of the present invention, when the directions of the electrical signal connections on the upper and lower surfaces of the piezoelectric element are reversed, a conductive adhesive is used for the purpose of coupling the conductive stiffening element to the piezoelectric element.

[0272] Surface B is the interface between the middle reference element 506 and the stiffening element 304. That is, B non-conductively couples the stiffening element to the middle reference element. There is no conductive structure on the middle reference element on this surface.

[0273] Surfaces D, E, F, G, H, and I are coupled via a non-conductive epoxy adhesive or other non-conductive binder, and one or more sections of these surfaces are left free from the adhesive for the purpose of electrically connecting or coupling different conductive structures on or within the elements in contact at said surfaces.

[0274] Surfaces J and M are coupled via a non-conductive epoxy adhesive or other non-conductive binder, and sections of these surfaces are left free from the adhesive for the purpose of electrically connecting or coupling different conductive structures on or within the elements in contact at said surfaces.

[0275] In an alternative embodiment of the present invention, surfaces J and K are coupled via a conductive epoxy adhesive or other conductive binder, or via soldering. Surfaces L and M are coupled via a conductive epoxy adhesive or other conductive binder, or via soldering.

[0276] In an alternative embodiment of the present invention, surfaces J and M are bonded together via a nonconductive epoxy adhesive or other nonconductive binder, leaving sections of these surfaces free from the adhesive for the purpose of electrically connecting or bonding different conductive structures on or within elements in contact with the surfaces.

[0277] In a preferred embodiment of the present invention, one or more of the upper, middle, and lower reference elements are made of non-conductive glass fiber, polyimide, PPS, or PE.

[0278] In a preferred embodiment of the present invention, the extension member is positioned on a central axis along the width of the piezoelectric element at a distance of 0 to 500 μm from the longitudinal end of the lower piezoelectric element. It is then bonded to the element via an epoxy adhesive film.

[0279] In this disclosure, all epoxy adhesive or binder films preferably have a thickness of 0.5 to 60 μm. Furthermore, the term binder may refer to cyanoacrylate, acrylic, epoxy, urethane, or polyimide-based adhesives.

[0280] Figure 7b shows a diagram of the drive signal applied to an actuator over time according to one embodiment of the present invention. Specifically, different voltages, deflections, and switching states are shown on the vertical axis, and time is shown on the horizontal axis. The values ​​and scales are illustrative and do not represent any specific scale.

[0281] Hereinafter, the common input voltage is defined as V, and in one embodiment of the present invention, it corresponds to the value of the variable high voltage provided to the upper surface of the upper piezoelectric element by the first high voltage line.

[0282] Vt represents an input signal corresponding to a variable high voltage value provided to the upper surface of the upper piezoelectric element by a first high voltage line in one embodiment of the present invention.

[0283] In one embodiment of the present invention, Vb represents an input signal corresponding to a variable high voltage value provided to the lower surface of the lower piezoelectric element by a second high voltage line.

[0284] In a preferred embodiment of the present invention, the input voltage is provided by a high voltage signal generation unit, and the common value of Vt and Vb corresponds when V0 is applied without voltage, and V n represents the maximum applicable positive voltage, and V -n is discretely switchable between n states representing the maximum applicable negative voltage. Note that any number n of intermediate voltages are possible between V -n and V n FIG. 7b is simplified for better understanding.

[0285] In an alternative embodiment of the present invention, the values of Vt and Vb are individually addressable.

[0286] In an alternative embodiment of the present invention, the values of Vt and Vb are individually addressable for each piezoelectric element.

[0287] The minimum change between the closest discretely addressable values of V is preferably 0.5 to 10 volts, more preferably 1 to 7 volts, and most preferably 1.5 to 5.5 volts.

[0288] The preferred maximum voltage is ±20 to ±150 volts, more preferably ±45 to ±105 volts. And the number of discrete voltage steps is freely variable according to the closest discretely addressable value of V.

[0289] TPD corresponds to the lateral d31 mode deflection of the upper piezoelectric element.

[0290] BPD corresponds to the lateral d31 mode deflection of the lower piezoelectric element.

[0291] SG1 corresponds to the switching ground line in the connected state, enables the flow of current to the grounded electrode of the corresponding piezoelectric element, and thereby enables the generation of an electromagnetic field.

[0292] The electrode elements of a piezoelectric element cause deflection, which is caused by the respective positive or negative values ​​of the substantially generated high-voltage signal.

[0293] SG0 corresponds to the switching ground line in the disconnected state, preventing current flow to the grounded electrode of the corresponding piezoelectric element, thereby stopping the generation of an electromagnetic field between the electrode elements of the piezoelectric element and effectively stopping any deflection caused by any positive or negative value of the generated high-voltage signal.

[0294] In this specification, actuator deflection refers to the deflection of the reference point at the free end of the actuator. That is, it refers to the deflection of the free end of the actuator to which the extension member according to the present invention is provided.

[0295] AD generally corresponds to orthogonal actuator deflection and broadly to the deflection of the stiffening element. Note that Figure 7b shows the deflection in a simplified form. Depending on the temporal actuator dynamics, the actual deflection may differ, and may have a more sinusoidal appearance in particular.

[0296] PDT defines a positive deflection threshold, which is the distance of downward deflection over a given period relative to the highest position of the actuator's deflection required to eject the liquid through the generation of pressure in the pressurized region. PDT depends on the rheological properties of the material being ejected and requires a specific positive deflection to be achieved within a given period for the material to be successfully ejected.

[0297] NDT defines a negative deflection threshold, which is the amount of upward deflection of the actuator relative to its lowest position over a given period of time, required to ensure priming or refilling of the dispensing region with the liquid material. NDT depends on the rheological properties of the dispensing material and requires a specific negative deflection to be achieved within a certain period of time for successful priming or refilling of the material.

[0298] Depending on the time scale, the deflection of the actuator may roughly correspond to the displacement graph shown in Figure 7b. Figure 7b simply shows, but is not exhaustive, the displacement modes achievable with different configurations of electrical signals that may be supplied to one or more piezoelectric elements at a given time.

[0299] At higher frequencies, as the actuator deflection approaches the harmonic frequency of the actuator system, the actuator deflection with respect to time may take on a more sinusoidal shape.

[0300] Using higher voltages or multiple piezoelectric elements generally results in faster acceleration and greater displacement than using lower voltages and a single piezoelectric element.

[0301] This allows for a wider range of controllable displacement acceleration, velocity, and deceleration that can be achieved over longer periods of time. Therefore, the discharge threshold for a particular material depends on the overall displacement and the acceleration and deceleration rates at which the displacement occurs.

[0302] The preferred maximum deflection of the free end of the actuator from a stationary position where no voltage is applied to any high-voltage line is ±0.4 μm to ±25 μm, more preferably ±0.9 μm to ±17.5 μm.

[0303] The preferred values ​​for PDT and NDT are 0.8 μm to 40 μm, more preferably 1 μm to 30 μm.

[0304] The rise time and fall time are shown on the horizontal axis as t, which is the amount of time required for the deflection to complete under the corresponding deformation of either the applied voltage or the piezoelectric ceramic element.

[0305] The preferred rise time t is 0.5 μs to 120 μs, more preferably 0.8 μs to 85 μs.

[0306] Location status n and AD -n The difference between, i.e., Δ AD n AD -nThe mean deflection velocity v is obtained by dividing this by time Tn. n Define the mean deflection velocity v. n This can generally be controlled by the delta between the deflections of the corresponding piezoelectric ceramic elements during the switching of the displacement voltage, where the larger the delta between the deformations, the greater the v n The value of this value is generally high.

[0307] The voltage applied to one piezoelectric element always acts in the opposite direction to the polarization of the other piezoelectric element when the voltage is positive or negative for both elements, thereby causing the maximum deflection of the piezoelectric ceramic element when the maximum positive or negative voltage is applied.

[0308] A preferred vn is 0.025 μS to 100 μS, more preferably 0.1 μS to 37.5 μS, and most preferably 0.21 μS to 8 μS.

[0309] The rise time t associated with the operation in which the maximum voltage is applied to both piezoelectric ceramic elements and the switching of the input signal causes the maximum difference between the applied displacements in both piezoelectric ceramic elements is further v n This causes the maximum value to be achieved.

[0310] Furthermore, the temporal shaping of deflection acceleration, speed, and deceleration, in other words, actuator deflection, can be controlled by a shaped electronic input signal, i.e., a waveform, where the voltage experienced by one or more piezoelectric elements may increase or decrease gradually or abruptly, thus affecting the deflection speed accordingly.

[0311] By applying differential voltage to the upper and lower piezoelectric elements, more precise control of actuator deflection and subsequent pressurization becomes possible, as shown in Figure 7b.

[0312] By freely changing the voltage rather than using discrete values, more precise shaping of the actuator deflection becomes possible.

[0313] In an alternative embodiment of the present invention, pulse width modulation of one or more input signals for the upper and lower piezoelectric elements is used for more precise shaping of the actuator deflection.

[0314] Figure 8 shows an actuator block 701 according to one embodiment of the present invention, viewed from an isometric angle. The actuator block 701 includes a plurality of actuator units, preferably 32 to 96 units. Furthermore, a conductive structure 511 on or inside the upper PCB element 503 is shown.

[0315] In one embodiment of the present invention, 32 units are preferred because the manufacturing and quality characteristics of the block can be well controlled by the small amount of piezoelectric elements present, and furthermore, the high-voltage drive electronic equipment (e.g., high-voltage shift register) can be addressed to either 8 or 32 channels, and thus the corresponding drive electronic equipment located outside the print head can be supplied to facilitate the construction of a variable print head length.

[0316] The core concept of the present invention is that actuator blocks can be manufactured in advance, and any number of actuator blocks can be connected to form an actuator assembly having a scalable number of actuator units.

[0317] In an alternative embodiment of the present invention, the print head consists of a single actuator block.

[0318] Figure 9 shows an actuator assembly according to one embodiment of the present invention from an isometric angle viewpoint. The actuator assembly 702 includes a plurality of actuator stacks 701, preferably three stacks.

[0319] Pumping operation

[0320] Figure 10a shows a schematic side view of a print head according to a first embodiment of the present invention having an extension member in the neutral position, and Figure 10b shows a schematic side view of a print head according to a first embodiment of the present invention having an extension member in the deflection position.

[0321] In other words, the extension member 401 is also in a neutral position and does not compress the discharge channel. Figures 10a and 10b further show the discharge region 607 within the discharge channel 603 and the nozzle opening 201 below the end of the extension member 401. A membrane element 203 is provided between the end of the extension member 401 and the discharge region 607.

[0322] Figure 10b shows a schematic side view of a print head according to one embodiment of the present invention having a piezoelectric element in a deflected position. Specifically, the extension member 401 moves downward, compressing the ejection channel 603 and generating pressurization of the liquid material present in the pressurized region 608.

[0323] In other words, a downward displacement of the actuator unit is shown, which elastically deforms the membrane element 203, positively pressurizing the discharge region 607, thereby creating a virtual chamber (not shown) within the surrounding pressurized region 608 in the discharge channel 603.

[0324] The aforementioned pressurization is key to the ejection of high-viscosity materials and enables the ejection of liquid materials with rheological properties unsuitable for conventional inkjet systems.

[0325] The discharge of the material is achieved through directional pressurization of the liquid material present within the aforementioned pressurized region 608 in the discharge channel. This pressurization requires achieving a pressure difference between the virtual chamber 609 and the ambient pressure on the opposite side of the nozzle plate.

[0326] The applicants recognized that in the system according to the present invention, a pressure difference needs to be maintained for a period of about 0.5 microseconds or longer in order to allow sufficient material flow for droplet formation and discharge of material with an Oh value greater than 2.3. Oh is the Ohnesorge number.

[0327] In conventional systems, it is impossible to eject materials with an Oh value significantly exceeding 2.3 with a relatively low back pressure difference relative to the surroundings and without using a jetting valve. The highest Oh value achievable within the prior art of conventional inkjet systems is achieved by utilizing a multi-pulse ejection method.

[0328] The aforementioned multiple pulse discharge method requires a much more complex waveform and is limited in terms of the rheological properties of the discharged liquid material, particularly the strong viscoelastic response of the material at high frequencies.

[0329] The effect of discharging materials exceeding this Oh value is definitively made possible by prolonged pressurization, which is induced by the displacement of the actuator, and most of the displacement of the actuator occurs at a speed lower than the speed of sound of the liquid medium being discharged.

[0330] This type of operation can be called non-acoustic or pumping operation, and in the system according to the present invention, an Oh value of approximately 8 or 9 can be achieved.

[0331] Molded membrane

[0332] Figure 11a shows a schematic side view of a print head according to a second embodiment of the present invention, and Figure 11b shows a print head according to a second embodiment of the present invention viewed from an isometric projection upward viewpoint.

[0333] Figure 11a shows one embodiment of the present invention, in which a molded membrane element 204 is depicted. The element is preferably attached to an extension member 401, or to a lower intermediate plate 613 preferably attached to the lower end of the extension member. The molded membrane is preferably attached via an adhesive.

[0334] In related embodiments, the extension member may have a reduced or partially reduced diameter at its lower end to accommodate a membrane formed in the through portion. The formed membrane is preferably attached via an adhesive. The reduction in diameter creates a reduced-diameter lower surface of the extension member, which comes into direct contact with the formed portion of the membrane that forms the new lower surface of the actuator and interacts with the fluid below.

[0335] Therefore, the displacement of the extension member 401 mainly leads to equal displacement of the central molded portion of the molded membrane, thus more efficiently transmitting displacement energy and pressurization in the central pressurized region 608, closely surrounding the virtual chamber and thus pressurizing liquid material that is not present in the vicinity of the virtual chamber, without losing energy by displacing the portion of the membrane surrounding the lower membrane surface.

[0336] Figure 11b shows a different viewpoint of the molded membrane shown in Figure 11a. The membrane is molded to surround the substantially cylindrical end of the extension member and the lower intermediate plate which is provided to have a circular shape.

[0337] In a preferred embodiment of the present invention, film formation is facilitated by thermal deformation of the material sheet or by ablation of the material sheet.

[0338] The reduced-diameter extension member or lower intermediate plate that is in direct contact with the molded film has a diameter of preferably 300 to 700 μm, more preferably 400 μm, at the bottom of the reduced-diameter extension member, compared to the original diameter of preferably 700 to 1000 μm, more preferably 800 μm.

[0339] In an alternative embodiment of the present invention, to facilitate a simpler method of bonding the upper end of the extension member, the diameter reduction may occur only in a partial section of the extension member. The diameter reduction is the same as the overall diameter reduction mentioned above.

[0340] That is, in a preferred embodiment of the present invention, the reduction in the diameter of the extension member, whether full or partial, is in the range of 50 to 75%, more preferably about 63%, compared to the diameter of the upper end of the extension member 401 in other described embodiments.

[0341] Displacement of nozzle plate

[0342] Figure 12a shows a schematic side view of a print head according to the first embodiment of the present invention having an extension member in a deflected position, and Figure 12b shows a schematic side view of a print head according to the first embodiment of the present invention having an extension member in a deflected position.

[0343] Specifically, Figures 12a and 12b show a closer side view of the print head with a cross-section aligned with the direction of the piezo actuator, where downward displacement of the actuator unit occurs, and further displacement of the nozzle plate occurs.

[0344] Furthermore, Figure 12a shows the displaced nozzle plate 610. This displacement occurs as a secondary effect of pressurization in the area below the lower extension member surface. The displacement of the nozzle plate is much smaller than the displacement of the actuator and is exaggerated for visibility in the drawing. The applicants recognized that the deformation of the nozzle plate affects the material present on the lower surface of the nozzle plate, i.e., the discharge side.

[0345] The displacement of the nozzle plate helps to release droplets that are still in contact with the nozzle plate. This displacement is strongly related to the fluid communication between the lower surface of the extension member and the nozzle plate, and the distance between them.

[0346] The nozzle plate elastically follows downward displacement in relation to the ambient pressure on the lower surface of the plate in response to pressure accumulation above the plate, and also follows upward displacement in relation to the overall decrease in pressure relative to the aforementioned internal pressurized state or general ambient pressure.

[0347] This displacement is directly correlated to the distance of the nozzle plate relative to the underside of the actuator in the pressurized and neutral position. This secondary displacement affects droplet ejection by causing surface perturbations in the droplet filament, generally assisting in the release of droplets from the ejection orifice.

[0348] In one embodiment of the present invention, the maximum nozzle plate displacement is approximately 0.1 to 4 μm, in relation to an actuator displacement of approximately 2 to 60 μm.

[0349] Figure 12b shows the elongated filament 614 of the extruded material. The filament may make droplet extrusion impossible for certain materials. The filament is generally associated with a higher viscosity or higher viscoelastic response of the liquid material under dynamic extrusion conditions.

[0350] Once these filaments are formed, they have the ability to break in different regimes. The fracturing regimes of the fluid filaments are generally named the atomizing regime, the first and second wind-induced regimes, the Rayleigh regime, or the dripping regime.

[0351] Droplet deposition is irrelevant due to the lack of material acceleration from the discharge orifice; the most relevant regime is generally the Rayleigh regime for single droplet generation for precise droplet deposition.

[0352] The aforementioned Rayleigh fracture, due to surface perturbations on the fluid thread surface, achieves droplet separation or pinch-off from the fluid thread, causing Rayleigh plateau instability, where the perturbation increases with the length of the fluid thread, thinning the fluid thread to a single point at some point, which causes fracture into one or more droplets.

[0353] This fluid filament breakage may become impossible if there is insufficient kinetic energy in the extruded material, causing the fluid filament not to reach a length that allows for pinch-off, or the rheological properties of the material to make pinch-off unfavorable, which is more likely to occur in high-viscosity or viscoelastic materials, or in materials extruded under conditions characterized by a high Weber number.

[0354] As shown in Figure 12b, the secondary effect of the displaced nozzle plate during discharge causes surface perturbations to the fluid threads during discharge, which helps pinch off the droplets and leads to stable droplet release.

[0355] This further facilitates pinch-offs that occur at regular time intervals in relation to the initial material ejection, thereby ejecting single droplets of high-viscosity material with high regularity.

[0356] The aforementioned time interval is generally determined by the pressure exerted on the material present in the pressurized region between the lower surface of the actuator and the nozzle plate, and this pressure is related to the distance between the lower surface of the actuating element and the upper surface of the nozzle plate.

[0357] It has been found that certain distances from the lower extension member surface 606 or alternatively from the lower film surface to the upper surface of the nozzle plate lead to stable dispensing for most materials under certain viscosity upper limits, which occur particularly at distances of 80-90 μm and 180-200 μm between the elements.

[0358] The dominant effect is the transfer of kinetic energy due to large actuator displacement, which is more important in the dispensing of high-viscosity materials, while secondary effects are generally more important in the dispensing of materials that have further rheological properties that hinder material dispensing.

[0359] The upper limit of energy discharge is approximately 380 mPa·s at the time of discharge for materials having more favorable rheological properties for achieving pinch-off, and approximately 350 mPa·s for materials having less favorable properties for pinch-off.

[0360] Properties of liquid materials that are generally less desirable for achieving pinch-off include higher material viscosity, higher viscoelastic response at lower frequency pressurization of the material, lower surface tension under certain conditions in the higher viscosity region, and lower material density under certain conditions in the higher viscosity region.

[0361] Furthermore, smaller nozzle diameters and lower discharge speeds are generally less desirable for dispensing high-viscosity materials, especially in cases where the material is primarily actuated acoustically.

[0362] The primary pressurization of the actuator in this invention generally occurs at a speed lower than the speed of sound in the liquid material present in the pressurized region; therefore, it is a pumping action rather than an acoustic action.

[0363] Some of the actuator's displacement may or may not occur at speeds higher than the speed of sound in the initial stages of operation, and therefore can be treated as an acoustic interaction.

[0364] Due to the extended pressurization resulting from the large displacement of the actuator that occurs over a longer period of time, the material is transported through the nozzle opening primarily by pressurization, rather than as an effect of acoustic waves interacting with pendant drops present on the outer surface of the meniscus or the underside of the nozzle conduit or nozzle plate.

[0365] The aforementioned pressurization directly controls the size and velocity of the droplets, and secondarily controls thread rupture and droplet release, and is generally influenced by the rate and range of actuator displacement.

[0366] According to the present invention, the speed and range are addressable to shape the acceleration and distance of the actuator displacement using a variable voltage and a switchable ground line.

[0367] Alternative actuator shapes

[0368] Figure 13a shows a print head according to the third embodiment of the present invention viewed from an isometric projection upward viewpoint, and Figure 13b shows a schematic side view of the print head according to the third embodiment of the present invention.

[0369] Specifically, as described in the above embodiment, the print head has two rows of actuator assemblies. The actuator assemblies are mirror images of each other and are arranged in parallel. This forms two rows of parallel extension members that interact with two corresponding discharge manifolds. In this embodiment, there is one inlet and one outlet channel for each of the discharge manifolds.

[0370] Figure 14 shows a cross-sectional view of a print head according to the fourth embodiment of the present invention.

[0371] In the embodiment of Figure 14, which relates to the embodiments of Figures 13a and 13b, the central channel is a shared channel, and the channel may be an inflow channel or an outflow channel depending on the desired flow direction of the material.

[0372] Figure 15 shows a cross-sectional view of a print head according to the sixth embodiment of the present invention.

[0373] In the embodiment shown in Figure 15, the rows of actuator assemblies share a single discharge manifold, effectively connecting each pair of corresponding extension members via corresponding discharge channels.

[0374] Figure 16a shows a print head according to the seventh embodiment of the present invention as viewed from an isometric projection upward viewpoint, and Figure 16b shows a cross-sectional view of the print head according to the seventh embodiment of the present invention.

[0375] In the embodiments shown in Figures 16a and 16b, a molded trimorph bender actuator is provided. The molded trimorph bender actuator includes a horizontally tapered stack of upper and lower piezoelectric elements, and a reinforcing element, as described above.

[0376] The elements generally taper from the end connected to the reference element toward the end where the extension member is provided, allowing two opposing actuator assemblies to be connected in a zip-like arrangement to form a single row of extension members. Each extension member preferably has an associated corresponding discharge channel, which is preferably narrowed in width.

[0377] The embodiments and some modifications of the present invention are described and illustrated above. The terms, descriptions and figures used herein are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art will recognize that many modifications are possible within the spirit and scope of the invention. The present invention is intended to be defined by the following claims and their equivalents, where all terms are understood in their broadest reasonable sense unless otherwise specified. [Explanation of symbols]

[0378] Printhead assembly 102 Electrical Connectors 103 Material Inlet Connector 104 Material Outlet Connector 106 Case Elements 107 Main fluid plate 109 Nozzle Plate 110 Membrane fastening element 111 First Vacuum Connector 112 Second Vacuum Connector Discharge side 201 Nozzle opening 202 Spacing Elements 203 Membrane elements 204 Molded membrane elements 205 Extension member through opening 206 Transmembrane opening 207 Heating Plate Actuator Assembly 301 Actuator 302 Upper piezoelectric element 303 Lower piezoelectric element 304 Reinforcement elements 305 Upper clamp element 306 Lower clamp element 401 Extension member 403 Extension member reference element Actuator mounting section 501 Heating plate connection element 502 Upper PCB plate 503 Intermediate PCB Plate 504 Lower / Bottom PCB Plate 505 Top Reference Element 506 Intermediate reference element 507 Bottom reference element 508 First High Voltage Line 509 Second High Voltage Line 510 Grand Line 511 Conductive structure Fluid element 601 Fluid inlet channel 602 Fluid Outlet Channel 603 Material Discharge Channel 604 Inflow connection point 605 Outflow connection point 606 Lower surface of extension member 607 Discharge area 608 Pressurized area 609 Virtual Chamber 610 Displaced nozzle plate 611 First Bypass Structure 612 Second Bypass Structure 613 Lower intermediate plate 614 Extended droplet filament Stacking of actuator units 701 Actuator Block 702 Actuator Assembly

Claims

1. A method for operating a print head actuator unit, The actuator unit comprises a first piezoelectric element connected to a first potential and a third potential, and a second piezoelectric element connected to a second potential and the third potential. The actuator unit is configured to deflect when the first potential and the second potential have the same polarity with respect to the third potential. The method involves applying a first variable high voltage Vt between the first potential and the third potential, and applying a second variable high voltage Vb between the second potential and the third potential. This includes applying a switchable ground connection to the third potential, method.

2. The first variable high voltage Vt and the second variable high voltage Vb are the same variable high voltage, preferably a positive or negative voltage. The method according to claim 1.

3. The first variable high voltage Vt and the second variable high voltage Vb are discretely switchable between n states. The method according to claim 1 or claim 2.

4. n is between 2 and 200, preferably between 3 and 150. The method according to claim 3.

5. The aforementioned switchable ground connection has two states, a) A first state in which the ground connection is in a connected state, allowing current to flow from the respective first potential and second potential to generate an electric field in each piezoelectric element, thereby causing deformation of the piezoelectric element, preferably d31 mode deformation, b) A second state in which the ground connection is disconnected, which prevents current from flowing from the respective first and second potentials, thereby preventing the generation of an electric field in each piezoelectric element and causing deformation. The method according to any one of claims 1 to 4.

6. The maximum upward deflection ADn corresponds to the ground connection state and the maximum positive voltages Vb and Vt. The maximum downward deflection AD.n corresponds to the ground connection state and the maximum negative voltages Vb and Vt. The method according to claim 5.

7. The average deflection velocity vn is defined by the positional difference between ADn and AD.n, which is obtained by dividing the positional difference between ADn and AD.n by the rise time t required to reach the maximum deflection state after switching on each voltage. Preferably, vn is between 0.025 μm / μs and 100 μm / μs, and more preferably between 0.2 μm / μs and 37.5 μm / μs. The method according to claim 6.

8. The maximum second voltage Vbn and the maximum first voltage Vtn are 20 to 250 volts, preferably 40 to 200 volts. The method according to any one of claims 1 to 7.

9. ET is defined as the downward deflection ejection threshold for material ejection from the print head, preferably ET is 0.3 μm to 40 μm, and more preferably 1 μm to 30 μm. The method according to any one of claims 1 to 8.

10. PT is defined as the refill threshold of the printhead in an upward deflection where the ejection area is filled with the material to be ejected, preferably PT is 0.3 μm to 40 μm, more preferably 1 μm to 30 μm. The method according to any one of claims 1 to 9.

11. The first and second voltages and ground connection states are selected such that the actuator unit maintains a deflection state of ET or higher for a period of 0.2 to 75 microseconds. The method according to claim 9 or claim 10.

12. The first and second voltages and ground connection states are selected such that the actuator unit maintains a deflection state of PT or higher for a period of 0.2 to 70 microseconds. The method according to claim 10 or claim 11.

13. The first and second voltages and the ground connection state are selected so that the actuator unit deflects at an average deflection speed of 0.025 μm / μs to 100 μm / μs. The method according to any one of claims 1 to 12.

14. The first and second voltages and the ground connection state are selected such that the displacement of the actuator is less than the speed of sound of the liquid material ejected from the print head. The method according to any one of claims 1 to 13.

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